Method of making brittle cathodes



I0 Drawing.

Patented Feb. 23, 1932 UNITED STATES PATENT OFFICE HARRY H. STOUT, 33., O1 NEW YORK, AND WILLIAM H. OSBOBN, Oil. GARBISON, YORK, ASSIGN'OKS '1'0 COPPER DEOKIDATIOH CORPORATION, '01 NEW .YORK, N. Y,

A. CORPORATION OF NEW YORK moi) or mine BRITTLE camonns This invention relatesto a new and im- A proved method for the electrolytic refining of metals. v

The principal object of the invention is to provide a method that will produce a copr cathode deposit that is coarsely crystaline and brittle, so that it is easily fran ble. This result is achieved by coating-t e surface against which the copper is to be deposited with afilm of material suitable to roduce the desired result.

e brittle co per deposit can easil be stripped from the coated surface, an reduced to small lumps that can be economically handled in subsequent operations.

A further advantage of the rocess lies in the savings that can be eflecte in the operation of the electrolytic process itself.

These and other objects and advantages of the invention will become apparent as the description proceeds.

While preferred methods of carrying outthe invention are disclosed herein, it will be understood that various changes may be made in the process without departing from the spirit and scope of the invention as here-' inafter set forth and claimed.

In current practice of electrolytic refining of co per the object is to obtain a deposit that is as tough as possible, and several ex- 1 edientsv are used to further that purpose.

bus in present multiple systems practice, two important steps are employed. .First, small quantities of glue are added to the electrolyte, which has the effect of increasing the degree of adhesiveness or cohesiveness between the deposited crystals andlhence making the whole deposit tough. Second, thedeposit is made on both sides of a thin, specially .prepared electrolytically deposited starting s eet towhich the de oslt adheres, forming a sheet ofdouble thic ess deposition cemented together by the starting sheet. The whole, i. e., deposit plus starting sheet, forming a threely heavy cathbdefis melted up-as one catho e in further treatment.

This system presents certain definite tank room disadvantages, among which may be listed: J

1st, The expense of making starting sheets.

Application and September is, 1929. Serial Io. seam.

presence of glue which increases the resistance and/or polarization of the electrolyte.

3rd. The increased sistance of the loops y. sheets are suspended from the cathode supportlng rod and to overcome contact resist ance, between supporting rod and loop.

4th. The thin starting sheets have a tendency to warp, causing short circuits against the anode with consequent loss of power and increased cost of inspection labor to prevent their forming.

\ In the present process, it not being necessary to form a tough deposit, glue is preferably omitted from the electrolyte and a relatively hea other suita le material, replaces the light starting sheet. The blank is reusable and hence is firmly fixed to the cathode supporting rod, eliminating the resistance of cathode suspending loop and loop contacts. Warp in is done awaywith.

blank of hard rolled copper, or

2nd. The increased power required due to ower to overcome rewhich the starting n the preferred form the process of this invention is carried out as a multiple process 1n the following manner:

A. A suitable blank of i suitable metal, preferably of hard rolled copper of suflicient v thickness to stand the abuse of average handling without denting, bending or warping (approximately has been found suitable) is cut to the desired dimensions and firmly attached to the cathode suspending rod so as to eliminate contact resistance at this point.

B. The blank is then coated with a suitable film to produce the desired brittle deposit. A preferred coating is a film of asphalt, whlch may be conveniently applied by dipping at a suitable temperature, the

blank in a solution or emu sion of asphalt. When this emulsion driesit leaves a very thin,tra-nsparent film of asphalt with a strong adhering power and high dielectric strength.

C. The blank coated as above is placed in the electrolytic tank and; deposit is made.

The electrolyte may be of usual composition, 7 4

except that as explained above glue is preferably omitted. Goulac, or any other similar organic compound ordinarily usedto promote eveness of distribution may be used if desired.

D. When the deposit has reached a suitable thickness, the cathode is lifted from the tank and the deposit stripped from the blank by any preferred means such as rapping the blank with a hammer, stripping with any form of stripping instrument or blade operated either by hand or mechanically, or by any other suitable means.

E. The deposit stripped from the blank is then broken up to desired particle size by shattering on the floor and passing through a grizzly, or by breaking in a trundle barrel,

or by any other suitable means.

The blanks are then ready for a repetition of the cycle of coating and deposition.

The copper deposited by this method is so brittle that a 14 day deposit, using 16 amperes per square foot current density can easily be broken by the fingers of a bare hand into pieces of approximately inch in diameter. After breaking up,the particles vary from inch up to 1 or more inchesin diameter, with very few fine particles, which are to be avoided as tending to cause copper losses in subsequent handling.

It is not the intention to limit the process to any particular theory of operation, but it is believed that the production of the brittle deposit can be explained in the following each other as the deposit grows out and the crystals increase in size-and the final result will be a cathode composed of crystals relatively loosely adhering on the electrolyte side of the deposit, but firmly held together by the tough skin formed in the first period of depositlon when the crystals, or crystal foci, were still very fine.

' In the process of the present invention the I coating used places between the blank and the electrolyte a continuous film opposed to the passage of current. As the current pierces this film at relatively separated points copper is deposited and crystals are formed which grow to relatively large size before coming irto contact with-their neighbors, and hence the crystals never adhere very closely to each other. Obviously too impervious a film will prevent deposit altogether and an insufficiently impervious fihn will not produce the desired effect. When using a coating substance that is fluid at the temperature of the electrolyte, the coating substance must have a correct balance of the three following factors 1. Viscosity ofthe ftuid.This controls the thickness of the film when immersed in electrolyte.

2. Power of wetting, or adhering, to the copper blanlcand hence preventing displacement of the substance by electrolyte at surface of blank.In general the power of hydrocarbons to wet and adhere to the blank is greater with those high in unsaturates and less with those low in unsaturates. The iodine number of an oil is a rough indication of its degree of unsaturation, hence of its wetting power.

3. Dielectric strength of the filming substanee.The higher. the dielectric strength, other factors being equal, the greater the resistance to current passage.

In the case of a coating substance that is solid at the temperature of the electrolyte, such as some waxes, or a thin film of asphalt the first two factors are automatically taken care of, and the degree of resistance of the film is regulated by the amount of coating substance applied. A continuous, solid film of wax of very high dielectric gives a very brittle deposit even when applied very thin.

Corn oil, when used as a coating material, gives a very brittle deposit. This is a highly fluid oil of low viscosity, that forms a thin film, but is of very high wetting power and high dielectric.

On the other hand, a high dielectric cable oil will give a tough deposit. This oil is of medium viscosity and very high dielectric, but it is composed of almost completely saturated hydrocarbons, and hence is of very low wetting or adhering power.

Ordinary double distilled rosin oil also gives a fairly tough deposit. This oil is of medium viscosity and good adhering power, but low dielectric.

Among other substances that have been found to yield a brittle deposit when correctly used, the following may be enumerated; linseed oil, sulphonated corn oil, crude fuel oil, cerowax made by the Vacuum Oil Company, superlowax made by the Standard Oil Company of Indiana. The invention contemplates the use of any coating substance that will produce the desired result, and these coating substances may be applied in different conditions, such as in various degrees of solution, in combination with a neutral agent or a beneficial agent, or in an emulsion form where, the substances can be emulsified. The coating substances can be applied in the most practical manner, as by dipping, painting, swabbing, spraying, etc.

The power saving of this process over common practice has been found, in comparative runs in a semi-commercial unit, to be approximately 15% of the total power used. This saving and the saving in labor in preparing starting sheets and in inspection against warping, considerably over-balances the cost of copper tie-up in the blanks and the cost of applying coating to the blanks, both necessary with the new process, so that the net saving per ton of cathode produced by the multiple system by the new processis considerable.

All cathodes on removal from the electrolyte carry on their surfaces, and between crystal faces, certain impurities which are in cluded in the electrolyte and adhere with it to the copper. Such impurities include slimes suspended in the electrolyte and such compounds as copper, iron and nickel sulphates 7 dissolved in the electrolyte, and also certain arsenic compounds, etc. In the present practice tough cathode sheets are dipped. in or 0 sprayed with some solution, usually hot water, to wash off as much as is practicable of these adherent impurities before further treatment. v

It has been found that the loosely adhering crystals of brittle cathode deposit are more permeable to the washing action of hot water, or acid or alkaline solutions, or other suitable solutions. than is tough cathode material a d that by percolation or agitation of a wash ihg solution through the granular mass of loosely adherent cathode crystals, it" is possible to obtain a more thorough degree of washing at less expense than can be done by spraying or dipping of tough cathode sheets.

The economical production of brittle cathode is important in connection with any process of refining where it is desired to bale the cathode into billets for subsequent treatment.

Those skilled in the art will recognize that the new process disclosed herein has many advantages, and they will appreciate the fact that the novel features are also applicable to the series process of electrolytic refining. It will also be understood that the process can be applied to the electrolytic deposition of other metals, such as zinc. v

. We claim 1. The process of electrolytic deposition of copper which includes coating a blank with a film of asphalt, inserting the blank in a bath of electrolyte and passing an electric current through the electrolyte between the blank and an anode, the asphalt film being of such thickness and properties that copper is deposited against it from the electrolyte in'a brittle deposit. 3 2. That step in the process of electrolytic deposition of copper which comprises dipping a blank in an emulsion of asphalt and subsequently drying the emulsion to cover the blank with a film of asphalt.

3. The process of electrolytic depositionof copper which includes coating a surface 5 upon which the copper is to be deposited with an embrittling filmcontaining unsaturated hydrocarbons, such dielectric strength that the current will pierce the film only at points that are separated from each other relatively widely to start building copper crystals, the embrittling film having suflicient Wetting power to surface during deposition but which can be readily stripped from the coated surface after deposition, and which is sufiiciently brittle to permit its being readily broken up into hunks after it is stripped from the coated surface.

- In testimony whereof we afiix our signatures. HARRY H. STOUT, JR. WILLIAM H. OSBORN.

the embrittling film having- 

